X-320M™ User's Manual
Appendix F: Methods and Calculation Details
Barometric Pressure
The Barometric Pressure reading is the instantaneous reading, no averaging is done. Once an hour, the
current Barometric Pressure is stored. This provides an hourly history for the past 24-hours.
By default, the station will give an absolute pressure reading. This reading is affected by the altitude of
the unit. By setting the Adjustment to Sea Level, the measurement is normalized to sea level with the
following equation. The user will still need to enter Slope and Offset values for the particular sensor
used.
Adjusted Pressure
=
p
∗
(
(
288
−
0.0065
∗
h
)
288
)
5.2561
p
= Barometric Pressure reading from the sensor in inches of Mercury
h
= Station elevation in meters
Calculated Values
The following values are not measured from any particular sensor; instead they are calculated based on
the information from several sensors.
Heat Index
Heat Index is based on Temperature and Humidity. The most recent instantaneous Temperature and
Humidity values are used for this calculation.
Heat Index will only be calculated when the Temperature is greater than or equal to 80ºF and the
Humidity is greater than or equal to 40% RH. Otherwise, the Heat Index will read the same as the
current Temperature.
The following equation is used to calculate the Heat Index:
Heat Index
=−
42.379
+(
2.04901523
∗
t
)+(
10.14333127
∗
rh
)
−(
0.22475541
∗
t
∗
rh
)−(
0.00683783
∗
t
2
)−(
0.05481717
∗
rh
2
)
+(
0.00122874
∗
t
2
∗
rh
)+(
0.00085282
∗
t
∗
rh
2
)−(
0.00000199
∗
t
2
∗
rh
2
)
t
= Temperature in Fahrenheit
rh
= Relative Humidity
Wind Chill
Wind Chill is based on Temperature and Wind Speed. The calculation uses the most recent temperature
measurement and the average Wind Speed, as shown on the
Status page
.
Wind Chill will only be calculated when the Temperature is below or equal to 50ºF and the Wind Speed
is greater than or equal to 3 mph. Otherwise, Wind Chill will read the same as the current temperature
The following equation is used to calculate the Wind Chill:
Wind Chill
=
35.74
+(
0.6215
∗
t
)−(
35.75
∗
w
0.16
)+(
0.4275
∗
t
∗
w
0.15
)
t
= Temperature in Fahrenheit
w
= Wind Speed in mph
Xytronix Research & Design, Inc.
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Summary of Contents for X-320m
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